Abstract
<p>The aim of this study was to evaluate and compare the antimicrobial properties of extracts of thirty commercial herbs and spices commonly used in the production of ready meals. Various extracts of spices were evaluated for their antimicrobial activities against <em>Escherichia coli</em>, <em>Listeria innocua</em>, <em>Staphylococcus aureus</em> and <em>Pseudomonas fluorescens</em><sup> </sup>using<strong> </strong>a<strong> </strong>microdilution broth method. Ethanol and hexane extracts of oregano, clove, sage, rosemary and celery showed relatively strong antimicrobial activities against all bacteria tested. In contrast, water extracts displayed little or no antimicrobial activity. Flow cytometry revealed that cell membrane structures were damaged by spice and herb active extracts, while analysis of intra- and extracellular ATP contents of bacteria indicated that an increase in extracellular ATP was partially due to intracellular leakage. Extract combinations assessed using the checkerboard method did not display synergistic effects, however, some additive effects were observed when oregano was combined with sage or rosemary against <em>L. innocua</em> or <em>S. aureus</em>. This study has demonstrated that some commercial spice extracts have antimicrobial activity against food-borne bacterial species and may be considered as potential antibacterial agents for addition to ready meals.</p>
Highlights
Food safety is a fundamental concern for both consumers and food producers alike
We have previously reported on microbiological status of commercial herbs and spices used in the manufacture of ready meals (Witkowska, Hickey, Alonso-Gomez, & Wilkinson, 2011) and subsequently we undertook this study in order to evaluate antimicrobial properties of concentrated extracts against selected food-borne bacteria for future potential application in reduced sodium ready meals
The results demonstrate that the choice of solvent used to extract herbs and spices had a significant influence on antimicrobial activities
Summary
Despite the high degree of awareness of food preservation methods there is increasing occurrence of disease outbreaks caused by pathogenic and spoilage microorganisms in foods (Meng & Doyle, 1998). Some ready meal manufacturers add synthetic antimicrobial agents such nitrates, nitrites, benzoates to inhibit the growth of food spoilage and food pathogenic microorganisms (Gould, 1996). Consumer awareness and concern that synthetic chemical additives may have some toxic or even carcinogenic effects, has increased the demand for high-quality, minimally processed foods with extended shelf-life, preferably free from or with a reduced level of added chemical antimicrobial agents (Zink, 1997). There has been an observed trend towards reducing salt levels in ready meals as a result of the proven association between excessive sodium intake, the development of hypertension and increased risk of cardiovascular disease (Desmond, 2006). There is growing interest in using natural antimicrobial compounds, including extracts of herbs and spices, as salt replacers or alternatives to synthetic compounds for food preservation (Smid & Gorris, 1999)
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